The invention relates to defining a time-variable property in digital compositions.
A digital composition typically has a sequence of frames, each containing data describing, for example, the audio or visual content of the frame. When the composition is played, the frames are sequentially output, and temporal changes in the composition are conveyed by the changing data in sequentially output frames.
A composition includes at least one layer. A layer also contains a sequence of frames containing data, such as audio or visual data, and generally may be individually created and edited. If the composition has more than one layer, the data from temporally corresponding frames of each layer are combined to form data for corresponding composition frames.
A time-variable property, such as the position of a layer, is generally defined by numeric values in a layer, and changes in that property over time are represented by changes in the property value in sequential layer frames. Traditionally, values for a time-variable property are defined for selected frames of the layer, referred to as key frames. To enable smooth changes of the property value, curve fitting based on the property values defined for the key frames determines a continuous curve defining property values for the intermediate frames between the key frames.
Properly defining property values over time requires a user to input values for individual key frames, and may require the user to create additional key frames to ensure that the fitted curve does not improperly define the property values in intermediate frames. Property definition can thus be a time consuming process.